Marion Island Marine Mammals in Changing Environments: Individual Heterogeneity and Population Processes

Abstract

This long term ecological research project addresses how individual variability in large mammals affects population processes. Long-term longitudinal studies focussing on large mammal populations are rare, and investigating population changes at these trophic levels are important indicators of environmental change. Critically, this research requires accurate identification and monitoring of individuals, measuring life history variables and understanding interactions between individuals, and their environment. Availability of resources in the Southern Ocean are closely linked to annual climatic variation, ultimately influencing top predator vital rates. Current long term studies of Marion Island’s top mammalian predators; southern elephant seals Mirounga leonina (SES), Subantarctic fur seals Arctocephalus tropicalis (SAFS), Antarctic fur seals A. gazella (AFS) and killer whales Orcinus orca (KW), facilitate observation of climate impacts. Mark-recapture in capital breeding SES investigates individual life-history. Body composition changes of SES individuals, a proxy for foraging success, are measured through photogrammetry, whilst satellite tracking of individuals identifies foraging variability. Dietary, hormonal and genetic profiles inform differential individual breeding and foraging of SES females. These investigations collectively aid in disentangling intrinsic and extrinsic drivers of individual heterogeneity. Income breeding sympatric populations of SAFS and AFS are assessed for a different scale of responses to environmental change through long-term dietary composition, individual foraging behaviour and breeding success. Potential top-down pressure on seal prey is investigated by intensive photographic mark-resight observation and foraging assessment of the local KW population.